Coke Strength & Tissue Compensators

Coke Strength and Fabric Compensators The strength of coke is its ability to withstand the various destructive loads (impact, abrading) that it undergoes during transport, overload, feed into the furnace and during melting. This property is considered the most important indicator of coke quality . Strong coke does not form fines, it allows to maintain high gas permeability of charge and high productivity of blast furnace. The strength of coke is determined by the artificial destruction of samples under the influence of shock and abrasive loads. A measure of strength is the change in the sieve (granulometric) composition of coke during the test and the use of tissue compensators. The most widely used method was to determine the strength of coke by destroying it in a rotating drum. This method consists in that a sample of coke of a certain size is placed inside a drum of a certain size, after which it is driven into rotation at a given speed for a set time. The pieces of coke are dragged up, falling, poured and, thus obtaining a share of shock and abrading loads, are destroyed to some extent depending on their mechanical strength. Strength is characterized by a change in the fineness of pieces of coke as a result of the test. In our country for a long time the standard method was to determine the strength of coke in a drum, proposed in Russia in the late nineteenth century E. Sundgrenom. The drum with a diameter of 2000 mm and a width of 800 mm has a cylindrical surface in the form of a grid of 25 mm diameter bars with the same compensators installed between them. A coke sample weighing 410 kg is loaded into the drum in pieces larger than 25 mm. The drum rotates for 15 minutes at a speed of 10 rpm. Formed as a result of the destruction of small pieces of coke fall into the gaps between the bars. The indicator of strength is the mass of coke left inside the drum. An additional characteristic is the amount of a 10-0 mm fraction in the concave product. Many years of practice showed that the normal operation of blast furnaces is possible on coke, which gives a residue in the drum of not less than 300 kg. The best varieties have a drum test of 340-350 kg. Similar test methods were used in many countries, however, the size of the drums, the weight of the sample, the number of revolutions were different. This led to incommensurability of coke strength indicators and the results of blast furnaces operation on them. Therefore, since 1963 in the USSR, the described method of Sundgren has been replaced by an international method for determining the strength of coke in a small closed drum with a diameter and length of 1000 mm (GOST 8929-65). On the inner surface of the drum are welded 4 corners with a height of 100 mm. For the test take a test of coke larger than 60 mm in an amount of 150 kg, which is divided into 3 parts with a mass of 50 kg. The drum is loaded with one of these parts (50 kg) and rotated at 25 rpm for 4 minutes. The sample is then removed and dispersed on sieves with round holes of 40 and 10 mm in diameter. The strength of coke is characterized by a yield of a fraction of +40 mm (M40 index), and its abrasion is the yield of a fraction of 10-0 mm (M10 index) as a percentage of the mass of the sample. Two samples are tested. In the event of a discrepancy in the results for M40 of more than 3% and for M10 more than 1%, the third test is tested. The final result is defined as the arithmetic mean. The higher the M40 and below M10, the stronger the coke. In recent years, in many plants, the strength of coke is tested in the same (small) drum (according to GOST 5953-72), with the same mode of loading and rotation, but for testing take a coke with a size of +25 mm. The indicator of the strength of coke is the output of the fraction +25 mm (M25), and the abrasion is M10. The average value of these indicators of coke strength in 1985 in factories in the South of the USSR varied within the following limits: M25 - from 70.7 to 88.9%; M10 - from 6.3 to 11.3%, and in factories in Russia and Kazakhstan: M40 - from 57.8 to 75.1%; M25 - from 83.7 to 87.6% and M10 - from 6.5 to 10.0%. In addition to the above methods for determining the strength of blast-furnace coke, others are used. The disadvantage of all these methods of testing the strength of coke in the cold state is that they can not evaluate its strength at high temperatures, to which the coke is heated in a blast furnace. Attempts are being made to develop a method for determining the thermal stability of coke. The strength of coke depends to a large extent on the number and shape of cracks in its pieces. The destruction of pieces occurs on the cracks, places of internal stresses that arise during the coking process. Studies have shown that the change in the coke's granulometric composition is not proportional to the applied fracture work: first, coke is rapidly crushed, the number of fine fractions increases sharply, while the large fractions sharply decrease, then the crushing slows down. The subsequent increase in the work of destruction leads mainly to the abrasion of coke, since crushing over the whole piece is difficult. This allowed us to evaluate the strength of coke according to the stabilized sieve composition obtained after the realization of all cracks and internal stresses. The extraction of coke from the blast furnace furnace via tuyeres showed that its sieve composition approximately corresponds to this stabilized composition. It is known that the gas permeability of fabric compensators of bulk lump materials improves with an increase in the uniformity of the dimensions of its lumps. In order to increase the homogeneity of coke in size with the production of pieces of the optimal size for blast furnaces (25-40 mm), attempts are made to preliminarily stabilize its sizing composition by exposing it to a certain amount of mechanical stress, followed by the screening of the formed small fractions. This will reduce the further destruction of pieces of coke with the formation of fines in the blast furnace and improve the gas permeability of the charge in its high-temperature zones.